Factor 'E,' isolated from E. coli and required for the stability of DNA-synthesizing complex, confers properties of the complex on free DNA polymerase I. The major quantity of natural complex in E. coli appears to be membrane-associated and new techniques for the isolation of this species are described. Factor 'E' is shown to be polymorphic. Techniques to manipulate interconversion of different forms are being explored to aid in the isolation of 'E'.